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                <ol class="chapter"><li class="chapter-item expanded affix "><a href="../翻译说明.html">翻译说明</a></li><li class="chapter-item expanded affix "><a href="../introduction.html">介绍</a></li><li class="chapter-item expanded "><a href="../notation.html"><strong aria-hidden="true">1.</strong> 表义符</a></li><li class="chapter-item expanded "><a href="../lexical-structure.html"><strong aria-hidden="true">2.</strong> 词法结构</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../input-format.html"><strong aria-hidden="true">2.1.</strong> 输入格式</a></li><li class="chapter-item expanded "><a href="../keywords.html"><strong aria-hidden="true">2.2.</strong> 关键字</a></li><li class="chapter-item expanded "><a href="../identifiers.html"><strong aria-hidden="true">2.3.</strong> 标识符</a></li><li class="chapter-item expanded "><a href="../comments.html"><strong aria-hidden="true">2.4.</strong> 注释</a></li><li class="chapter-item expanded "><a href="../whitespace.html"><strong aria-hidden="true">2.5.</strong> 空白符</a></li><li class="chapter-item expanded "><a href="../tokens.html"><strong aria-hidden="true">2.6.</strong> token</a></li></ol></li><li class="chapter-item expanded "><a href="../macros.html"><strong aria-hidden="true">3.</strong> 宏</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../macros-by-example.html"><strong aria-hidden="true">3.1.</strong> 声明宏</a></li><li class="chapter-item expanded "><a href="../procedural-macros.html"><strong aria-hidden="true">3.2.</strong> 过程宏</a></li></ol></li><li class="chapter-item expanded "><a href="../crates-and-source-files.html"><strong aria-hidden="true">4.</strong> crate 和源文件</a></li><li class="chapter-item expanded "><a href="../conditional-compilation.html"><strong aria-hidden="true">5.</strong> 条件编译</a></li><li class="chapter-item expanded "><a href="../items.html"><strong aria-hidden="true">6.</strong> 程序项</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../items/modules.html"><strong aria-hidden="true">6.1.</strong> 模块</a></li><li class="chapter-item expanded "><a href="../items/extern-crates.html"><strong aria-hidden="true">6.2.</strong> 外部crate</a></li><li class="chapter-item expanded "><a href="../items/use-declarations.html"><strong aria-hidden="true">6.3.</strong> use声明</a></li><li class="chapter-item expanded "><a href="../items/functions.html"><strong aria-hidden="true">6.4.</strong> 函数</a></li><li class="chapter-item expanded "><a href="../items/type-aliases.html"><strong aria-hidden="true">6.5.</strong> 类型别名</a></li><li class="chapter-item expanded "><a href="../items/structs.html"><strong aria-hidden="true">6.6.</strong> 结构体</a></li><li class="chapter-item expanded "><a href="../items/enumerations.html"><strong aria-hidden="true">6.7.</strong> 枚举</a></li><li class="chapter-item expanded "><a href="../items/unions.html"><strong aria-hidden="true">6.8.</strong> 联合体</a></li><li class="chapter-item expanded "><a href="../items/constant-items.html"><strong aria-hidden="true">6.9.</strong> 常量项</a></li><li class="chapter-item expanded "><a href="../items/static-items.html"><strong aria-hidden="true">6.10.</strong> 静态项</a></li><li class="chapter-item expanded "><a href="../items/traits.html"><strong aria-hidden="true">6.11.</strong> trait</a></li><li class="chapter-item expanded "><a href="../items/implementations.html"><strong aria-hidden="true">6.12.</strong> 实现</a></li><li class="chapter-item expanded "><a href="../items/external-blocks.html"><strong aria-hidden="true">6.13.</strong> 外部块</a></li><li class="chapter-item expanded "><a href="../items/generics.html"><strong aria-hidden="true">6.14.</strong> 泛型参数</a></li><li class="chapter-item expanded "><a href="../items/associated-items.html"><strong aria-hidden="true">6.15.</strong> 关联程序项</a></li></ol></li><li class="chapter-item expanded "><a href="../attributes.html"><strong aria-hidden="true">7.</strong> 属性</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../attributes/testing.html"><strong aria-hidden="true">7.1.</strong> 测试</a></li><li class="chapter-item expanded "><a href="../attributes/derive.html"><strong aria-hidden="true">7.2.</strong> 派生</a></li><li class="chapter-item expanded "><a href="../attributes/diagnostics.html"><strong aria-hidden="true">7.3.</strong> 诊断</a></li><li class="chapter-item expanded "><a href="../attributes/codegen.html"><strong aria-hidden="true">7.4.</strong> 代码生成</a></li><li class="chapter-item expanded "><a href="../attributes/limits.html"><strong aria-hidden="true">7.5.</strong> 极限值设置</a></li><li class="chapter-item expanded "><a href="../attributes/type_system.html"><strong aria-hidden="true">7.6.</strong> 类型系统</a></li></ol></li><li class="chapter-item expanded "><a href="../statements-and-expressions.html"><strong aria-hidden="true">8.</strong> 语句和表达式</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../statements.html"><strong aria-hidden="true">8.1.</strong> 语句</a></li><li class="chapter-item expanded "><a href="../expressions.html"><strong aria-hidden="true">8.2.</strong> 表达式</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../expressions/literal-expr.html"><strong aria-hidden="true">8.2.1.</strong> 字面量表达式</a></li><li class="chapter-item expanded "><a href="../expressions/path-expr.html"><strong aria-hidden="true">8.2.2.</strong> 路径表达式</a></li><li class="chapter-item expanded "><a href="../expressions/block-expr.html"><strong aria-hidden="true">8.2.3.</strong> 块表达式</a></li><li class="chapter-item expanded "><a href="../expressions/operator-expr.html"><strong aria-hidden="true">8.2.4.</strong> 运算符表达式</a></li><li class="chapter-item expanded "><a href="../expressions/grouped-expr.html"><strong aria-hidden="true">8.2.5.</strong> 分组表达式</a></li><li class="chapter-item expanded "><a href="../expressions/array-expr.html"><strong aria-hidden="true">8.2.6.</strong> 数组和索引表达式</a></li><li class="chapter-item expanded "><a href="../expressions/tuple-expr.html"><strong aria-hidden="true">8.2.7.</strong> 元组和索引表达式</a></li><li class="chapter-item expanded "><a href="../expressions/struct-expr.html"><strong aria-hidden="true">8.2.8.</strong> 结构体表达式</a></li><li class="chapter-item expanded "><a href="../expressions/call-expr.html"><strong aria-hidden="true">8.2.9.</strong> 调用表达式</a></li><li class="chapter-item expanded "><a href="../expressions/method-call-expr.html"><strong aria-hidden="true">8.2.10.</strong> 方法调用表达式</a></li><li class="chapter-item expanded "><a href="../expressions/field-expr.html"><strong aria-hidden="true">8.2.11.</strong> 字段访问表达式</a></li><li class="chapter-item expanded "><a href="../expressions/closure-expr.html"><strong aria-hidden="true">8.2.12.</strong> 闭包表达式</a></li><li class="chapter-item expanded "><a href="../expressions/loop-expr.html"><strong aria-hidden="true">8.2.13.</strong> 循环表达式</a></li><li class="chapter-item expanded "><a href="../expressions/range-expr.html"><strong aria-hidden="true">8.2.14.</strong> 区间表达式</a></li><li class="chapter-item expanded "><a href="../expressions/if-expr.html"><strong aria-hidden="true">8.2.15.</strong> if 和 if let 表达式</a></li><li class="chapter-item expanded "><a href="../expressions/match-expr.html"><strong aria-hidden="true">8.2.16.</strong> 匹配表达式</a></li><li class="chapter-item expanded "><a href="../expressions/return-expr.html"><strong aria-hidden="true">8.2.17.</strong> 返回表达式</a></li><li class="chapter-item expanded "><a href="../expressions/await-expr.html"><strong aria-hidden="true">8.2.18.</strong> 等待(await)表达式</a></li></ol></li></ol></li><li class="chapter-item expanded "><a href="../patterns.html"><strong aria-hidden="true">9.</strong> 模式</a></li><li class="chapter-item expanded "><a href="../type-system.html"><strong aria-hidden="true">10.</strong> 类型系统</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../types.html"><strong aria-hidden="true">10.1.</strong> 类型</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../types/boolean.html"><strong aria-hidden="true">10.1.1.</strong> 布尔型</a></li><li class="chapter-item expanded "><a href="../types/numeric.html"><strong aria-hidden="true">10.1.2.</strong> 数字型</a></li><li class="chapter-item expanded "><a href="../types/textual.html"><strong aria-hidden="true">10.1.3.</strong> 字符型</a></li><li class="chapter-item expanded "><a href="../types/never.html"><strong aria-hidden="true">10.1.4.</strong> never类型</a></li><li class="chapter-item expanded "><a href="../types/tuple.html"><strong aria-hidden="true">10.1.5.</strong> 元组</a></li><li class="chapter-item expanded "><a href="../types/array.html"><strong aria-hidden="true">10.1.6.</strong> 数组</a></li><li class="chapter-item expanded "><a href="../types/slice.html"><strong aria-hidden="true">10.1.7.</strong> 切片</a></li><li class="chapter-item expanded "><a href="../types/struct.html"><strong aria-hidden="true">10.1.8.</strong> 结构体</a></li><li class="chapter-item expanded "><a href="../types/enum.html"><strong aria-hidden="true">10.1.9.</strong> 枚举</a></li><li class="chapter-item expanded "><a href="../types/union.html"><strong aria-hidden="true">10.1.10.</strong> 联合体</a></li><li class="chapter-item expanded "><a href="../types/function-item.html"><strong aria-hidden="true">10.1.11.</strong> 函数项类型</a></li><li class="chapter-item expanded "><a href="../types/closure.html"><strong aria-hidden="true">10.1.12.</strong> 闭包</a></li><li class="chapter-item expanded "><a href="../types/pointer.html"><strong aria-hidden="true">10.1.13.</strong> 指针型</a></li><li class="chapter-item expanded "><a href="../types/function-pointer.html"><strong aria-hidden="true">10.1.14.</strong> 函数指针</a></li><li class="chapter-item expanded "><a href="../types/trait-object.html"><strong aria-hidden="true">10.1.15.</strong> trait对象</a></li><li class="chapter-item expanded "><a href="../types/impl-trait.html"><strong aria-hidden="true">10.1.16.</strong> 实现trait</a></li><li class="chapter-item expanded "><a href="../types/parameters.html"><strong aria-hidden="true">10.1.17.</strong> 类型参数</a></li><li class="chapter-item expanded "><a href="../types/inferred.html"><strong aria-hidden="true">10.1.18.</strong> 推断型</a></li></ol></li><li class="chapter-item expanded "><a href="../dynamically-sized-types.html"><strong aria-hidden="true">10.2.</strong> 动态尺寸类型(DST)</a></li><li class="chapter-item expanded "><a href="../type-layout.html"><strong aria-hidden="true">10.3.</strong> 类型布局 </a></li><li class="chapter-item expanded "><a href="../interior-mutability.html"><strong aria-hidden="true">10.4.</strong> 内部可变性</a></li><li class="chapter-item expanded "><a href="../subtyping.html"><strong aria-hidden="true">10.5.</strong> 子类型和型变</a></li><li class="chapter-item expanded "><a href="../trait-bounds.html"><strong aria-hidden="true">10.6.</strong> trait约束及其生存期约束</a></li><li class="chapter-item expanded "><a href="../type-coercions.html"><strong aria-hidden="true">10.7.</strong> 类型自动强转</a></li><li class="chapter-item expanded "><a href="../destructors.html"><strong aria-hidden="true">10.8.</strong> 析构函数</a></li><li class="chapter-item expanded "><a href="../lifetime-elision.html"><strong aria-hidden="true">10.9.</strong> 生存期省略</a></li></ol></li><li class="chapter-item expanded "><a href="../special-types-and-traits.html"><strong aria-hidden="true">11.</strong> 特殊类型和 trait</a></li><li class="chapter-item expanded "><a href="../names.html"><strong aria-hidden="true">12.</strong> 名称</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../names/namespaces.html"><strong aria-hidden="true">12.1.</strong> 命名空间</a></li><li class="chapter-item expanded "><a href="../names/scopes.html"><strong aria-hidden="true">12.2.</strong> 作用域</a></li><li class="chapter-item expanded "><a href="../names/preludes.html" class="active"><strong aria-hidden="true">12.3.</strong> 预导入包</a></li><li class="chapter-item expanded "><a href="../paths.html"><strong aria-hidden="true">12.4.</strong> 路径</a></li><li class="chapter-item expanded "><a href="../names/name-resolution.html"><strong aria-hidden="true">12.5.</strong> 名称解析</a></li><li class="chapter-item expanded "><a href="../visibility-and-privacy.html"><strong aria-hidden="true">12.6.</strong> 可见性与隐私权</a></li></ol></li><li class="chapter-item expanded "><a href="../memory-model.html"><strong aria-hidden="true">13.</strong> 内存模型</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../memory-allocation-and-lifetime.html"><strong aria-hidden="true">13.1.</strong> 内存分配和生存期</a></li><li class="chapter-item expanded "><a href="../variables.html"><strong aria-hidden="true">13.2.</strong> 变量</a></li></ol></li><li class="chapter-item expanded "><a href="../linkage.html"><strong aria-hidden="true">14.</strong> 链接(linkage)</a></li><li class="chapter-item expanded "><a href="../unsafety.html"><strong aria-hidden="true">15.</strong> 非安全性</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../unsafe-functions.html"><strong aria-hidden="true">15.1.</strong> 非安全函数</a></li><li class="chapter-item expanded "><a href="../unsafe-blocks.html"><strong aria-hidden="true">15.2.</strong> 非安全代码块</a></li><li class="chapter-item expanded "><a href="../behavior-considered-undefined.html"><strong aria-hidden="true">15.3.</strong> 未定义行为</a></li><li class="chapter-item expanded "><a href="../behavior-not-considered-unsafe.html"><strong aria-hidden="true">15.4.</strong> 不被认为是非安全的行为</a></li></ol></li><li class="chapter-item expanded "><a href="../const_eval.html"><strong aria-hidden="true">16.</strong> 常量求值</a></li><li class="chapter-item expanded "><a href="../abi.html"><strong aria-hidden="true">17.</strong> ABI</a></li><li class="chapter-item expanded "><a href="../runtime.html"><strong aria-hidden="true">18.</strong> Rust运行时</a></li><li class="chapter-item expanded "><a href="../appendices.html"><strong aria-hidden="true">19.</strong> 附录</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../macro-ambiguity.html"><strong aria-hidden="true">19.1.</strong> 宏定义规范</a></li><li class="chapter-item expanded "><a href="../influences.html"><strong aria-hidden="true">19.2.</strong> 影响来源</a></li><li class="chapter-item expanded "><a href="../glossary.html"><strong aria-hidden="true">19.3.</strong> 术语表</a></li><li class="chapter-item expanded "><a href="../本书术语翻译对照表.html"><strong aria-hidden="true">19.4.</strong> 本书术语翻译对照表</a></li></ol></li></ol>
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                        <h1><a class="header" href="#preludes" id="preludes">Preludes</a></h1>
<h1><a class="header" href="#预导入包" id="预导入包">预导入包</a></h1>
<blockquote>
<p><a href="https://github.com/rust-lang/reference/blob/master/src/names/preludes.md">use-declarations.md</a><br />
commit: 83f725f1b9dda6166589d7b715b75b7f54143b8e <br />
本章译文最后维护日期：2021-07-31</p>
</blockquote>
<p><em>预导入包</em>是一组名称的集合，它会自动把这些名称导入到 crate 中的每个模块的作用域中。</p>
<p>预导入包中的那些名称不是当前模块本身的一部分：它们在<a href="name-resolution.html">名称解析</a>期间被隐式导入。例如，即使像 <a href="../../std/boxed/struct.Box.html"><code>Box</code></a> 这样在每个模块的作用域中到处使用的名称，你也不能通过 <code>self::Box</code> 来引用它，因为它不是当前模块的成员。</p>
<p>有几个不同的预导入包：</p>
<ul>
<li><a href="#standard-library-prelude">标准库预导入包</a></li>
<li><a href="#extern-prelude">外部预导入包</a></li>
<li><a href="#language-prelude">语言预导入包</a></li>
<li><a href="#macro_use-prelude"><code>macro_use</code>预导入包</a></li>
<li><a href="#tool-prelude">工具类预导入包</a></li>
</ul>
<h2><a class="header" href="#standard-library-prelude" id="standard-library-prelude">Standard library prelude</a></h2>
<h2><a class="header" href="#标准库预导入包" id="标准库预导入包">标准库预导入包</a></h2>
<p>标准库预导入包包含了 <a href="../../std/prelude/index.html"><code>std::prelude::v1</code></a>模块中的名称。如果使用<a href="#the-no_std-attribute"><code>no_std</code>属性</a>，那么它将使用<a href="../../core/prelude/index.html"><code>core::prelude::v1</code></a>模块中的名称。</p>
<h2><a class="header" href="#extern-prelude" id="extern-prelude">Extern prelude</a></h2>
<h2><a class="header" href="#外部预导入包" id="外部预导入包">外部预导入包</a></h2>
<p>在根模块中使用 <a href="../items/extern-crates.html"><code>extern crate</code></a> 导入的外部crate 或直接给编译器提供的的外部crate（也就是在 <code>rustc</code>命令下使用 <code>--extern</code>命令行参数选项）会被添加到<em>外部预导入包</em>中。如果使用 <code>extern crate orig_name as new_name</code> 这类别名导入，则符号 <code>new_name</code> 将被添加到此预导入包。</p>
<p><a href="../../core/index.html"><code>core</code></a> crate 总是会被添加到外部预导入包中。只要 <a href="#the-no_std-attribute"><code>no_std</code>属性</a>没有在 crate根模块中指定，那么<a href="../../std/index.html"><code>std</code></a> crate 就会被添加进来</p>
<blockquote>
<p><strong>版次差异</strong>：在 2015 版中，在外部预导入包中的 crate 不能通过 <a href="../items/use-declarations.html">use声明</a>来直接引用，因此通常标准做法是用 <code>extern crate</code> 将那它们纳入到当前作用域。</p>
<p>从 2018 版开始， <a href="../items/use-declarations.html">use声明</a>可以直接引用外部预导入包里的 crate，所以再在代码里使用 <code>extern crate</code> 就会被认为是不规范的。</p>
</blockquote>
<blockquote>
<p><strong>注意</strong>: 随 <code>rustc</code> 一起引入的 crate，如 <a href="../../alloc/index.html"><code>alloc</code></a> 和 <a href="../../test/index.html"><code>test</code></a>，在使用 Cargo 时不会自动被包含在 <code>--extern</code> 命令行参数选项中。即使在 2018 版中，也必须通过外部crate(<code>extern crate</code>)声明来把它们引入到当前作用域内。</p>
<pre><pre class="playground"><code class="language-rust edition2018">
<span class="boring">#![allow(unused)]
</span><span class="boring">fn main() {
</span>extern crate alloc;
use alloc::rc::Rc;
<span class="boring">}
</span></code></pre></pre>
<p>Cargo却会将 <code>proc_macro</code> 带入到编译类型为 proc-macro 的 crate 的外部预导入包中</p>
</blockquote>
<!--
查看 https://github.com/rust-lang/rust/issues/57288 以了解更多关于 alloc/test 的限制。
-->
<h3><a class="header" href="#the-no_std-attribute" id="the-no_std-attribute">The <code>no_std</code> attribute</a></h3>
<h3><a class="header" href="#no_std属性" id="no_std属性"><code>no_std</code>属性</a></h3>
<p>默认情况下，标准库自动包含在 crate根模块中。在 <a href="../../std/index.html"><code>std</code></a> crate 被添加到根模块中的同时，还会隐式生效一个 <a href="../macros-by-example.html#the-macro_use-attribute"><code>macro_use</code>属性</a>，它将所有从 <code>std</code> 中导出的宏放入到<a href="#macro_use-prelude"><code>macro_use</code>预导入包</a>中。默认情况下，<a href="../../core/index.html"><code>core</code></a> 和 <a href="../../std/index.html"><code>std</code></a> 都被添加到<a href="#extern-prelude">外部预导入包</a>中。<a href="#standard-library-prelude">标准库预导入包</a>包含了 <a href="../../std/prelude/index.html"><code>std::prelude::v1</code></a>模块中的所有内容。</p>
<p>*<code>no_std</code><a href="../attributes.html">属性</a>*可以应用在 crate 级别上，用来防止 <a href="../../std/index.html"><code>std</code></a> crate 被自动添加到相关作用域内。此属性作了如下三件事：</p>
<ul>
<li>阻止 <code>std</code> crate 被添加进<a href="#extern-prelude">外部预导入包</a>。</li>
<li>使用<a href="#standard-library-prelude">标准库预导入包</a>中的 <a href="../../core/prelude/index.html"><code>core::prelude::v1</code></a> 来替代默认情况下导入的 <a href="../../std/prelude/index.html"><code>std::prelude::v1</code></a>。</li>
<li>使用 <a href="../../core/index.html"><code>core</code></a> crate 替代 <a href="../../std/index.html"><code>std</code></a> crate 来注入到当前 crate 的根模块中，同时把 <code>core</code> crate下的所有宏导入到 <a href="#macro_use-prelude"><code>macro_use</code>预导入包</a>中。</li>
</ul>
<blockquote>
<p><strong>注意</strong>：当 crate 的目标平台不支持标准库或者故意不使用标准库的功能时，使用核心预导入包而不是标准预导入包是很有用的。此时没有导入的标准库的那些功能主要是动态内存分配（例如：<code>Box</code>和' <code>Vec</code>）和文件，以及网络功能（例如：<code>std::fs</code> 和 <code>std::io</code>）。</p>
</blockquote>
<div class="warning">
<p>警告：使用 <code>no_std</code> 并不会阻止标准库被链接进来。使用 <code>extern crate std;</code> 将 <code>std</code> crate 导入仍然有效，相关的依赖项也可以被正常链接进来。</p>
</div>
<h2><a class="header" href="#language-prelude" id="language-prelude">Language prelude</a></h2>
<h2><a class="header" href="#语言预导入包" id="语言预导入包">语言预导入包</a></h2>
<p>语言预导入包包括语言内置的类型名称和属性名称。语言预导入包总是在当前作用域内有效的。它包括以下内容：</p>
<ul>
<li><a href="namespaces.html">类型命名空间</a>
<ul>
<li><a href="../types/boolean.html">布尔型</a> — <code>bool</code></li>
<li><a href="../types/textual.html">文本型</a> — <code>char</code> 和 <code>str</code></li>
<li><a href="../types/numeric.html#integer-types">整型</a> — <code>i8</code>, <code>i16</code>, <code>i32</code>, <code>i64</code>, <code>i128</code>, <code>u8</code>, <code>u16</code>, <code>u32</code>, <code>u64</code>, <code>u128</code></li>
<li><a href="../types/numeric.html#machine-dependent-integer-types">和机器平台相关的整型</a> — <code>usize</code> 和 <code>isize</code></li>
<li><a href="../types/numeric.html#floating-point-types">浮点型</a> — <code>f32</code> 和 <code>f64</code></li>
</ul>
</li>
<li><a href="namespaces.html">宏命名空间</a>
<ul>
<li><a href="../attributes.html#built-in-attributes-index">内置属性</a></li>
</ul>
</li>
</ul>
<h2><a class="header" href="#macro_use-prelude" id="macro_use-prelude"><code>macro_use</code> prelude</a></h2>
<h2><a class="header" href="#macro_use预导入包" id="macro_use预导入包"><code>macro_use</code>预导入包</a></h2>
<p><code>macro_use</code>预导入包包含了外部crate 中的宏，这些宏是通过在当前文档源码内部的 <a href="../items/extern-crates.html"><code>extern crate</code></a> 声明语句上应用 <a href="../macros-by-example.html#the-macro_use-attribute"><code>macro_use</code>属性</a>来导入此声明中的 crate 内部的宏。</p>
<h2><a class="header" href="#tool-prelude" id="tool-prelude">Tool prelude</a></h2>
<h2><a class="header" href="#工具类预导入包" id="工具类预导入包">工具类预导入包</a></h2>
<p>工具类预导入包包含了在<a href="namespaces.html">类型命名空间</a>中声明的外部工具的工具名称。请参阅<a href="../attributes.html#tool-attributes">工具类属性</a>一节，以了解更多细节。</p>
<h2><a class="header" href="#the-no_implicit_prelude-attribute" id="the-no_implicit_prelude-attribute">The <code>no_implicit_prelude</code> attribute</a></h2>
<h2><a class="header" href="#no_implicit_prelude属性" id="no_implicit_prelude属性"><code>no_implicit_prelude</code>属性</a></h2>
<p>*<code>no_implicit_prelude</code><a href="../attributes.html">属性</a>*可以应用在 crate级别或模块上，用以指示它不应该自动将<a href="#standard-library-prelude">标准库预导入包</a>、<a href="#extern-prelude">外部预导入包</a>或<a href="#tool-prelude">工具类预导入包</a>引入到当前模块或其任何子模块的作用域中。</p>
<p>此属性不影响<a href="#language-prelude">语言预导入包</a>。</p>
<blockquote>
<p><strong>版次差异</strong>: 在 2015版中，<code>no_implicit_prelude</code>属性不会影响<a href="#macro_use-prelude"><code>macro_use</code>预导入包</a>，从标准库导出的所有宏仍然包含在 <code>macro_use</code>预导入包中。从 2018版开始，它也会禁止 <code>macro_use</code>预导入包生效。</p>
</blockquote>

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